1. Field of the Invention
The present invention relates to a semiconductor laser.
2. Description of the Prior Art
Various types of semiconductor lasers are proposed in the art for attaining a horizontal optical confinement in active regions.
For example, U.S. Pat. Nos. 3,978,428 and 4,033,796 and Japanese patent publication gazette No. 5273/1979 disclose a channeled substrate planar (CSP) structure. In such structure, both sides of an active layer are held by first and second clad layers, at least one of which has a thick central portion and thin end portions so as to penetrate a laser beam generated from both ends of the active layer through the thin portions of the clad layer to be absorbed by an optical absorption layer provided on the outer side of the clad layer, thereby to horizontally confine the laser beam.
In such structure, however, grooves must be formed in a substrate in order to vary the thickness of the clad layer or a clad layer once grown must be removed by etching.
A report by W. D. Laiding et al. in Appl. Phys. Lett. 38(10), May 15, 1981, pp. 776-778 describes that in quantum-well layer, a portion in which Zn (zinc) is diffused is different in band gap energy from that having no Zn diffusion.